Adaptive immunity Chapter 16

1
Adaptive immunityChapter 16
2
Third Line of Defense

• Is called adaptive immunity
• The bodys ability to recognize and defend itself
  against distinct invaders and their products
• Is a smart system whose memory allows it to
  respond rapidly to a second encounter with a
  pathogen
• Antigens trigger specific immune responses
• Various cells, tissues, and organs are part of
  specific immunity
• Includes B and T lymphocytes

3
Antigens

• Molecules that trigger a specific immune response
• Include components of bacterial cell walls,
  capsules, pili, and flagella, as well as proteins
  of viruses, fungi, and protozoa
• Food and dust can also contain antigenic
  particles
• Enter the body by various methods
• Through breaks in the skin and mucous membranes
• Direct injection, as with a bite or needle
• Through organ transplants and skin grafts

Animation Antigen Processing and Presentation
PLAY
4
Antigens
Figure 16.1
5
The Lymphatic System

• Screens the tissues of the body for foreign
  antigens
• Composed of lymphatic vessels and lymphatic cells

Figure 16.2
6
Lymphatic Vessels

• Form a one-way system that conducts lymph from
  local tissues and returns it to the circulatory
  system
• Lymph is a liquid with similar composition to
  blood plasma that arises from fluid leaked from
  blood vessels into surrounding tissues

7
Lymphoid Cells

• Develop from stem cells in the red bone marrow
• Includes lymphocytes, the smallest of the
  leukocytes

8
Lymphocytes
Figure 16.3
9
Lymph Node
Figure 16.4
10
Lymph Nodes

• Houses leukocytes that recognize and attack
  foreign antigens present in the lymph
• Concentrated in the cervical (neck), inguinal
  (groin), axillary (armpit), and abdominal regions
• Receives lymph from afferent lymphatic vessels
  and drains lymph into efferent lymphatic vessels

11
Other Lymphoid Tissues and Organs

• Spleen
• Similar in structure and function to the lymph
  nodes
• Filters bacteria, viruses, toxins, and other
  foreign matter from the blood
• Tonsils and mucosa-associated lymphoid tissue
  (MALT)
• Physically trap foreign particles and microbes
• MALT includes the appendix, lymphoid tissue of
  the respiratory tract, vagina, urinary bladder,
  mammary glands, and Peyers patches in the wall
  of the small intestine

12
B Lymphocytes

• Arise and mature in the red bone marrow
• Found primarily in the spleen, lymph nodes, and
  MALT
• Small percentage of B cells circulate in the
  blood
• Major function is the secretion of antibodies

13
Antibodies

• Also called immunoglobulins (Ig)
• Soluble proteins that bind antigen
• Secreted by plasma cells, which are B cells
  actively fighting exogenous antigen
• Considered part of the humoral immune response
  since bodily fluids such as lymph and blood were
  once called humors

14
Antibody Structure

• Antigen-binding sites are complementary to
  antigenic determinants (epitopes)

Figure 16.5
15
Functions of Antibodies

• Function in several ways
• Activation of complement
• Stimulation of inflammation
• Neutralization
• Opsonization
• Agglutination

Figure 16.6
16
Classes of Antibodies

• A single type of antibody is not sufficient for
  the multiple types of invaders to the body
• The class involved in the immune response depends
  on the type of foreign antigen, the portal of
  entry, and the antibody function needed
• Five different classes of antibodies

17
Classes of Antibodies
Figure 16.7
18
Characteristics of the Five Classes of
Immunoglobulins
Table 16.1
19
B Cell Receptor (BCR)

• Is an antibody that remains associated with the
  cytoplasmic membrane
• Each B lymphocyte has multiple copies of a single
  type of BCR
• Antigen binding site is identical to that of the
  secreted antibody for that particular cell
• The randomly generated antibody variable region
  determines the BCR (it is not formed in response
  to antigens)
• Each BCR is complementary to only one antigenic
  determinant
• The BCRs on all of an individuals B cells are
  capable of recognizing millions of different
  antigenic determinants

20
T Lymphocytes

• Produced in the red bone marrow and mature under
  the influence of the thymus
• Circulate in the lymph and blood and migrate to
  the lymph nodes, spleen, and Peyers patches
• Part of the cell-mediated immune response because
  they act directly against various antigens
• Endogenous invaders
• Many of the bodys cells that harbor
  intracellular pathogens
• Abnormal body cells such as cancer cells that
  produce abnormal cell surface proteins

21
T Cell Receptor
Figure 16.9
22
Cytotoxic T cells (TC Cells)

• Distinguished by the CD8 cell-surface
  glycoprotein
• Directly kill certain cells
• Cells infected with viruses and other
  intracellular pathogens
• Abnormal cells, such as cancer cells

23
Helper T Cells (TH Cells)

• Distinguished by the CD4 cell-surface
  glycoprotein
• Function to help regulate the activities of B
  cells and cytotoxic T cells during an immune
  response
• Secrete various soluble protein messengers,
  called cytokines, that determine which immune
  response will be activated

24
Helper T Cells (TH Cells)

• Two types
• Type 1 helper T cell (TH1)
• Assist cytotoxic T cells
• Express a cytokine receptor named CCR5
• Type 2 helper T cell (TH2)
• Assist B cells
• Have cytokine receptors CCR3 and CCR4

25
Cytokines

• Soluble regulatory proteins that act as
  intercellular signals when released from certain
  body cells
• Immune system cytokines signal among various
  leukocytes
• The complex web of signals among all the cell
  types of the immune system is referred to as the
  cytokine network

26
Cytokines of the Immune System

• Interleukins (ILs) signal among leukocytes
• Interferons (IFNs) antiviral proteins that may
  act as cytokines
• Growth factors proteins that stimulate stem
  cells to divide, maintaining a adequate supply of
  leukocytes
• Tumor necrosis factor (TNF) Secreted by
  macrophages and T cells to kill tumor cells and
  regulate immune responses and inflammation
• Chemokines signal leukocytes to go to a site of
  inflammation or infection and stimulate other
  leukocytes

27
Lymphocyte Editing by Clonal Deletion

• Vital that immune responses not be directed
  against autoantigens
• Body edits lymphocytes to eliminate any
  self-reactive cells

28
Lymphocyte Editing by Clonal Deletion
Figure 16.10
29
Major Histocompatibility Complex (MHC)

• Important in determining the compatibility of
  tissues in successful tissue grafting
• Major histocompatibility antigens are
  glycoproteins found in the membranes of most
  cells of vertebrate animals
• Function to hold and position antigenic
  determinants for presentation to T cells
• Antigens bind in the antigen-binding groove of
  MHC molecules
• Two classes of MHC proteins
• MHC class I
• MHC class II

30
MHC Two Classes
Figure 16.11
31
Antigen Processing

• T-independent antigen
• Large antigen molecules with readily accessible,
  repeating antigenic determinants
• B cells can bind these directly without being
  processed
• Stimulates B cells to differentiate into a plasma
  cell and produce antibodies

32
Antigen Processing

• T-dependent antigens
• Smaller antigens with less accessible antigenic
  determinants
• B cells require involvement from helper T cells
  to target these antigens
• Helper T cells are assisted by leukocytes that
  process the antigen to make the antigenic
  determinants more accessible
• Processing is different based on whether the
  antigen is exogenous or endogenous

33
Processing of Exogenous Antigens

• APC internalizes the invading pathogen and
  enzymatically digests it into smaller antigenic
  fragments which are contained within a
  phagolysosome
• Phagolysosome fuses with a vesicle containing MHC
  II molecules
• Each fragment binds to the antigen-binding groove
  of a complementary MHC II molecule
• The fused vesicle then inserts the MHC II-antigen
  complex into the cytoplasmic membrane so the
  antigen is presented on the outside of the cell

34
Processing of Endogenous Antigens

• The intracellular pathogens are also digested
  into smaller antigenic determinants
• Each fragment binds to a MHC I molecule located
  in the endoplasmic reticulum membrane
• The membrane is packaged into a vesicle by a
  Golgi body which is inserted into the cytoplasmic
  membrane so the antigen is displayed on the
  cells surface

35
Humoral Immune Response

• Body mounts humoral immune responses against
  exogenous pathogens
• Components of a humoral immune response
• B cell activation and clonal selection
• Memory B cells and the establishment of
  immunological memory

Animation Humoral Immunity
PLAY
36
Humoral Immune Response
Figure 16.14
37
Plasma Cells

• Make up the majority of cells produced during B
  cell proliferation
• Each plasma cell secretes only antibody molecules
  complementary to the specific antigenic
  determinant
• Are short-lived cells that die within a few days
  of activation, though their antibodies and
  progeny can persist

38
Memory B Cells

• Cells produced by B cell proliferation that do
  not secrete antibodies
• Cells that have BCRs complementary to the
  specific antigenic determinant that triggered
  their production
• Long-lived cells that divide only a few times and
  then persist in the lymphoid tissue
• Are available to initiate antibody production if
  the same antigen is encountered again

39
Primary and Secondary Responses
Figure 16.15
40
Cell-Mediated Immune Response

• Responds to intracellular pathogens and abnormal
  body cells
• The most common intracellular pathogens are
  viruses but the response is also effective
  against intracellular bacteria
• Triggered when antigenic determinants of the
  pathogen are displayed on the host cells surface

41
Activation of TC Cells
Figure 16.16
42
A Cell-Mediated Immune Response
Animation Cell-Mediated Immunity
PLAY
Figure 16.17
43
Acquired Immunity

• Specific immunity acquired during an individuals
  life
• Two types
• Naturally acquired- immune response against
  antigens encountered in daily life
• Artificially acquired- response to antigens
  introduced via a vaccine
• Further distinguished as either active or passive
• Active- active response to antigens via humoral
  or cell-mediated responses
• Passive- passively receive antibodies from
  another individual

44
A Comparison of the Types of Acquired Immunity
Table 16.3